Multi-stage flash distillation process

ABSTRACT

In a multi-stage flash distillation process, feed liquid to be distilled is progressively preheated by passage along a primary flow path in heat exchange relation with vapor zones of a series of successively staged flash evaporation chambers having flash liquid zones arranged in fluid communication. Flash liquid evaporated from the various flash liquid zones is replenished by feed liquid diverted from the primary flow path to and along secondary or by-pass flow paths leading directly to associated liquid zones. The liquid diverted to each secondary flow path has a temperature substantially equal to the temperature of the flash liquid in the zone to which it is diverted. When the liquid to be distilled contains scale forming materials which tend to precipitate at high temperatures, the liquid is preferably divided into a plurality of parts and at least one of the parts is treated with a suitable scale inhibitor. Feed liquid is tapped from the various parts to provide a plurality of streams of feed liquid which collectively comprise the primary flow path. At least some of the streams contain differing concentrations of scale inhibitor. Each stream is diverted from the primary flow path as aforedescribed when the preheated liquid in the stream attains a temperature slightly below the temperature at which scale deposition tends to occur.

Spicacci [54] MULTI-STAGE FLASH DISTILLATION PROCESS [76] Inventor:Attilio R. Spicacci, 22 Allen Street, New Britain, Conn.

[22] Filed: July 29, 1971 [21] Appl. No.: 167,366

[52] US. Cl. ..203/7, 202/ 173, 159/2 MS, 203/ 1 l [51] Int. Cl. ..B0ld3/00, BOld 3/10, BOld 3/02, BOld H28 [58] Field of Search ..202/173,174; 203/11, 10, 7; 159/2 MS [56] References Cited UNITED STATES PATENTS3 ,344,041 9/1967 Wulfson ..202/173 3 ,446,7 1 2 5/1969 Othmer ..202/1733,467,587 9/1969 Connell et al. ..202/173 3 ,486,985 12/ l 969 McGrath..202/173 3,489,652 1] 1970 Williamson... ..203/1 1 3,399,975 9/1968Otten ..203/7 X 3,476,654 11/ 1969 Sieder ..203/7 PrimaryExaminer-Norman Yudkoff e e! aamin rd fet. a V. Attorney Roger B.McCormick, Theodore R.

[ 1 May 22, 1973 In a multi-stage flash distillation process, feedliquid to be distilled is progressively preheated by passage along aprimary flow path in heat exchange relation with vapor zones of a seriesof successively staged flash evaporation chambers having flash liquidzones arranged in fluid communication. Flash liquid evaporated from thevarious flash liquid zones is replenished by feed liquid diverted fromthe primary flow path to and along secondary or by-pass flow pathsleading directly to associated liquid zones. The liquid diverted to eachsecondary flow path has a temperature substantially equal to thetemperature of the flash liquid in the zone to which it is diverted.When the liquid to be distilled contains scale forming materials whichtend to precipitate at high temperatures, the liquid is preferablydivided into a plurality of parts and at least one of the parts istreated with a suitable scale inhibitor. Feed liquid is tapped from thevarious parts to provide a plurality of streams of feed liquid whichcollectively comprise the primary flow path. At least some of thestreams contain differing concentrations of scale inhibitor. Each streamis diverted from the primary flow path as aforedescribed when thepreheated liquid in the stream attains a temperature slightly below thetemperature at which scale deposition tends to occur.

11 Claims, 6 Drawing Figures Patented May 22, 1973 2 Sheets-Sheet 1 FIG.4

INVENTOR. ATTILIO R. SPICACCI ATTQRNEYS Patented May 22, 1973 2Sheets-Sheet. 2

w 5 m J m m m com V:

MULTI-STAGE FLASH DISTILLATION PROCESS BACKGROUND OF THE INVENTION Thisinvention relates in general to multi-stage flash distillation processesand deals more particularly with improved processes particularly adaptedfor conversion of saline or brackish water to potable water.

In distillation processes of the aforedescribed general type feed liquidto be distilled is or may be progressively preheated by conveyance in aprimary flow path in heat exchange relation with vapor zones of amultistage flash evaporator. The preheated feed liquid is ultimatelyintroduced into the first stage of the evaporator where pressure issufficiently low to cause some of the feed liquid to flash or boilinstantly to produce steam in a vapor zone thereabove. Vaporization ofsome of the feed liquid in the liquid zone of the first stage results ina lowering of the temperature of the remaining liquid in the liquid zoneof that stage. This liquid then flows into the next successive chamberwhere some of the liquid flashes and the temperature and pressure of theremaining liquid is again reduced. Condensation occurs when theresulting steam or vapor contacts heat exchange surfaces which definethe primary flow path. In this manner, heat removed from the steam tocondense it serves to preheat incoming feed liquid. This process isrepeated in the apparatus as many times as is feasible. In a process ofthe aforedescribed type all of the feed liquid is usually raised to thetemperature of the flash liquid in the first stage of the evaporatorbefore being introduced into the evaporator, although successive stagesof the evaporator operate at substantially lower temperatures. Thepresent invention provides an improved process of the aforedescribedtype wherein distribution of feed liquid is improved to increase thermalefficiency.

When the liquid to be distilled contains scale forming materials whichtend to precipitate at high temperatures to form deposits on the wallsof vessels or tubes in which the feed liquid is contained or conveyedthe operating temperature range for the system is generally limited. Thetendency of scale formation to occur is further enhanced byconcentration of the brine solution as by evaporation. This problem isoften overcome by treating feed liquid with a suitable additive toinhibit scale formation in the higher temperature stages, however, nopractical benefit is derived from the inhibited feed liquid in thestages of the evaporator which operate at lower temperatures/The presentinvention provides a process which includes improved distribution offeed liquid for more efficient utilization of scale inhibitors and thelike.

SUMMARY OF THE INVENTION In accordance with the present invention animproved multi-stage flash distillation process is provided wherein feedliquid progressively preheated by passage along a primary flow path inheat exchange relation with vapor zones of successively staged flashevaporation chambers of a multi-stage flash evaporation apparatus isdiverted from at least one region of the primary flow path directly intoan associated flash liquid zone having a flash liquid temperaturesubstantially equal to the temperature of the feed liquid at said oneregion. In accordance with a further method of the invention feed liquidcontaining scale forming materials which tend to precipitate atdistillation temperatures is divided into parts and at least one of theparts is treated with a scale inhibitor. Feed liquid selectively tappedfrom the parts is fed through the apparatus in a plurality of streamswhich collectively comprise the primary flow path. At least some of thestreams contain differing concentrations of scale inhibitor. Each streamis diverted from the primary flow path directly into a flash liquid zonecontaining flash liquid at substantially the same temperature when thefeed liquid in the stream is preheated to a temperature slightly belowthe temperature at which precipitation of the scale forming materialstherein tends to occur.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic view illustratinga multi-stage flash distillation apparatus incorporating the process ofthe present invention.

FIG. 2 is a schematic flow diagram further'illustr-ating the process ofFIG. 1.

FIG. 3 is a schematic side elevational view of another multi-stage flashdistillation apparatus illustrating a further process of the presentinvention.

FIG. 4 is a fragmentary schematic bottom view of the distillationapparatus of FIG. 3.

FIG. 5 is a fragmentary flow diagram further illustrating the process ofFIG. 3.

FIG. 6 is a somewhat schematic side elevational view illustrating atypical arrangement of a single feed tube of the apparatus of FIG. 3.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to thedrawings and referring first particularly to FIG. 1, a multi-stage flashdistillation apparatus used in practicing a process of the presentinvention is illustrated somewhat schematically and designated generallyby the reference numeral 10. The apparatus 10, as illustrated, is usedin the distillation of sea water and comprises a series of forty-ninesuccessively staged flash evaporation chambers designated by encirclednumerals 1-49, respectively. Each evaporation chamber has a flash liquidzone 12, a vapor zone 14 and a condensation tray or the like designatedat 16 for collecting distillate obtained on condensation of vapor formedin the vapor zone. The liquid zones 12, 12 are in fluid communicationwith each other and provide a progressive flow path in one directionthrough the various chambers as indicated by the directional arrows inthe liquid zones (FIG. 1 The liquid zones 14, 14 of the various stages1-49 are maintained at temperatures which progressively decrease in thedirection of liquid flow therethrough. Makeup liquid which comprises seawater is conveyed into the apparatus through a conduit or line 17 to andalong a primary flow path indicated generally at 18. In the furtherdescription which follows, liquid which flows in the primary flow pathis designated feed liquid and may, for example, comprise makeup liquidor a mixture of makeup liquid and other liquid, such as recycle brine ormakeup liquid that has been treated with a suitable scale inhibitor. Theprimary flow path 18 passes progressively through at least some of thevapor zones 14, 14 in'heat exchange relation therewith and in thedirection opposite the direction of liquid flow through the liquidzones. In this manner the feed liquid is preheated as it flows along theprimary flow path 18 and vapor in the various vapor zones 14, 14 issimultaneously condensed. At least some of the feed liquid in theprimary flow path 18 passes through an external heater 20 where it isfurther heated prior to being conveyed into the liquid zones through aconduit 22. At least some of the preheated feed liquid is diverted fromthe primary flow path to and along a secondary or by-pass flow path anddirectly into an associated liquid zone having a temperaturesubstantially equal to the temperature of the liquid diverted thereto.The apparatus shown in FIG. 1 includes one such secondary flow path 24which communicates with the primary flow path 18 at one region 26located in one of the chambers 14, 14 and with the liquid zone ofanother of the chambers which has a temperature substantially equal tothe temperature of the feed liquid at the region 26. For convenience inillustrating the process, a valve 27 is shown associated with thesecondary flow path for regulating flow in the latter path. It should beunderstood that liquid flow in the secondary flow path is preferablyregulated by selecting tubes of a proper cross-sectional area to definethe secondary flow paths. Another external heating unit 28 is or may beemployed to preheat the liquid in the primary flow path 18 before it isconveyed into the apparatus 10, as will be hereinafter furtherdiscussed. Distillate or potable water obtained on a condensation ofvapor formed in the various vapor zones l4, l4 flows from the apparatusthrough a conduit 30. Brine formed on concentration of the feed liquidflows from the apparatus through another conduit 32. If desired, some ofthe brine may be recycled and for this purpose another conduit 34 isprovided which communicates with the conduit 32 and the primary flowpath 18.

A preferred arrangement of the process discussed with reference to FIG.1 is further illustrated by the schematic flow diagram of FIG. 2, theflash evaporation chambers being designated by encircled numerals 149,respectively. The flash temperature or the temperature of the liquid inthe liquid zone in various stages of the apparatus and the correspondingtemperatures attained by the preheated feed liquid in the latter stagesare respectively designated below and above the diagram. It will benoted that there is a 12 F differential between the temperature of theflashing brine and the temperature of the preheated feed liquid in eachof the designated stages. Thus, for example, at the seventh stage thetemperature of the flashing brine is 266 F whereas the temperature ofthe preheated feed liquid at that stage is 254 F. It will be furthernoted that the temperature of the brine decreases by 12 F as the brineflows progressively through each three successive stages. Thus, thetemperature of the flashing brine at the fourth stage is 278 F, whereasthe corresponding brine temperature at the seventh stage is 266 F. Aplurality of secondary flow paths are provided as indicated at 24a-24p.Each secondary flow path communicates with an associated region of theprimary flow path 18 and a flash liquid zone of substantially the sametemperature. Thus, for example, the secondary flow path 24b communicateswith the primary flow path 18 at region 26b within the fourth stage ofthe apparatus and with the flash liquid zone of the seventh stage todivert preheated feed liquid at a temperature of 266 F from the primaryflow path directly into a liquid zone maintained at substantially thesame temperature. The various other secondary flow paths which comprisethe system are arranged in substantially the same manner.

Flow in the various secondary or by-pass flow paths is regulated so thatfeed liquid converted into vapor in each group of three successivestages is replenished in the next successive stage by feed liquid whichflows directly from the primary flow path into the flash liquid zone ofthe latter stage. For example, flash liquid converted into vapor in thefourth, fifth and sixth stages is replenished in the seventh stage bypreheated feed liquid which flows directly from the fourth stage intothe flash liquid zone of the seventh stage. Sufficient pressure must bemaintained in the various flow paths to maintain suitable flow velocitythroughout the system and for this purpose the apparatus 10 may includeone or more circulating pumps (not shown). However, flow in the varioussecondary flow paths is preferably regulated so that feed liquid flowsfrom each secondary flow path into a respectively associated flashliquid zone without substantially altering internal pressure of theassociated stage into which the feed liquid flows. It will now beevident that the purpose of the preheating unit 28 is to raise thetemperature of the feed liquid in the primary flow path 18 so that thetemperature of the preheated feed liquid at 4th stage is substantiallyequal to the flash liquid temperature at the 49th or last stage of theapparatus 10. Thus, a substantially thermally balanced process isattained. It will be further evident that brine or flash liquid atvarious progressive stages of the process is constantly replenished andthereby diluted by the direct addition of feed liquid which hassubstantially the same temperature as the flash liquid. All of theforegoing factors contribute toe the maintenance of an efflcientwell-balanced process.

One of the more difficult problems in the distillation of sea water andthe like is prevention of scale formation on heat exchange surfaces.Scale formed in the distillation of sea water consists primarily ofcalcium carbonate, magnesium, hydroxide and various calcium sulfates,which remain in solution at ordinary temperatures, but which become lesssoluble at distillation temperatures. As the temperature of the feedliquid increases, these scale forming compounds tend to precipitateforming tenacious deposits on heat exchange surfaces of the distillationapparatus. The formation of scale may be prevented by reducing theoperating temperatures of the apparatus or by acidulation of the feedliquid as by the addition of a suitable scale inhibitor, as is wellknown in the art. The latter solution is generally preferable and, forthis reason, most commercial processes employed in the distillation ofsea water provide for some pretreatment of the feed water to inhibitscale formation. The present process provides means for effectingefflcient treatment and distribution of feed liquid.

Referring now particularly to FIGS. 3-5, another multi-stage flashdistillation apparatus used in practicing the present invention andparticularly adapted for use in the distillation of sea water isillustrated somewhat schematically and designated generally by thereference numeral 10a. Parts of the apparatus 10a similar to partspreviously described bear the same reference numerals and a letter a"suffix. The apparatus 10a includes a series of successively staged flashevaporation chambers each of which has a liquid zone 12a and a vaporzone (FIG. 5). The various liquid zones are in fluid communication witheach other and with the conduit 32a.

Raw sea water to be distilled enters the apparatus through a conduit orline 17a and passes through conventional heat reject stages designatedgenerally by the numeral 35. In this manner, the brine being dischargedfrom the system and the product water are used to preheat the incomingsalt water. The apparatus may, if desired, also include a deaerator ordecarbonator, such as indicated at 37 for pretreating the makeup liquid,as is well known in the art.

In accordance with the presently preferred method of practicing theinvention, makeup liquid or sea water to be distilled is mixed withrecycle liquid and divided into a plurality of parts and at least one ofthe parts is treated with a suitable scale inhibitor as, for example,acid. Thereafter, liquid is selectively tapped from the various parts toprovide a plurality of individual streams of feed liquid which are fedthrough the apparatus and which collectively comprise a primary flowpath.

In the illustrated apparatus a, the primary flow path 18a comprises aplurality of individual liquid streams designated Sl-Sl7. Each stream isformed by tapping liquid from at least one of three supply tanks orwater boxes designated at 36, 38 and 40. Due to the efficientutilization of scale inhibitors, initial stages of the present apparatusmay operate at relatively high temperatures. For this reason, anintermediate heater designated at 43 is or may be provided forincreasing the temperatures of the liquid streams S1-S7 before thesestreams are introduced into the higher temperature stages of theapparatus 10a. The apparatus 10a also has an auxiliary by-pass line 4which includes a valve 47. This auxiliary by-pass may be used to obtainan improved mass and heat balance in the system or may be used to effectpartial shut down of the system. A pump 42 conveys raw sea water througha preheater 28 and into the water box 38. Some of the sea water from thewater box 38 flows into the water box 36 where it is treated with asuitable scale inhibitor, as, for example, sulfuric acid to acidulate orneutralize it. Some of the brine discharged from the apparatus throughthe line 32a is pumped through the line 34a into the water box 40 forrecirculation through the apparatus as hereinafter described.

Referring particularly to FIGS. 4 and 5, it will be noted that the feedstream S1 receives treated sea water from the water box 36 and attains atemperature of 326 before being conveyed into the flash liquid zonesthrough the conduit 22a as shown in FIG. 5. The feed line S2 isconnected to each of the water boxes 36, 38 and 40 and receives a blendof makeup liquid therefrom particularly suited to be heated to 314 Fwithout precipitation. When the feed liquid in the stream S2 attains atemperature of 314, all of the liquid in that stream is diverted to andalong a secondary flow path 24a to a flash liquid zone havingsubstantially the same temperature, as best shown in FIG. 5. The makeupliquid in the stream S17 is subjected to much lower temperature and iscomprised entirely of recycled brine received from the water box 40, asbest shown in FIG. 4. All of the remaining streams S3-S17 compriseblends of feed liquid received from the various water boxes 36-40, theblend which comprises each stream being adapted to be heated to apredetermined temperature without the occurrence of scale formation. Animportant feature of the aforedescribed system is that each by-passfeedor secondary flow path serves to replenish the flashing brine evaporatedfrom an associated liquid zone with feed liquid of the same temperatureand salt concentration as that of the brine entering the flash liquidzone from the flash liquid zone of the preceding stage of the apparatus.Thus, an efficient process is maintained wherein abrupt changes intemperature and salt concentration may be wholly avoided or at leastsubstantially eliminated.

Multi-stage flash evaporation apparatus of the type hereinbeforedescribed with reference to the present process usually includes bundlesof tubes which extend through all stages of the apparatus to convey feedliquid therethrough. In the illustrated apparatus 10 and 10a, forconvenience of illustration, the various feed lines which convey streamsof makeup liquid through the apparatus are shown as individual feedlines or conduits, however, it should be understood that bundles oftubes will preferably be employed to convey makeup liquid through theapparatus, in a manner well known in the art.

In FIG. 6 a typical feed tube arrangement is shown which carries thestream S3. This feed tube is arranged to tap liquid from each of thewater boxes 36, 38 and 40 and to convey the resulting blend of feedliquid to the apparatus 10a. The latter feed tube supplies feed liquidto a bundle to tubes designated at 44 which convey the liquid in theprimary flow path 18a through various stages of the apparatus. It willbe noted that only the stream S1 extends through all stages of theapparatus. Each of the other streams S2-S17 respectively correspond to abundle of tubes which extend only partially through the various stagesof the apparatus 10a. Thus a substantial saving in the quantity ofcondenser tubing required to make the distillation apparatus may berealized in practicing the present processes.

In a conventional multi-stage flash evaporation apparatus of the typewell known in the art, all of the feed liquid passes progressivelythrough all of the vapor stages of the apparatus in heat exchangerelation therewith. However, in accordance with the method of thepresent invention, the quantity of feed liquid in the primary flow pathprogressively diminishes in the direction of flow through the variousstages of the apparatus due to the provision of the various by-pass orsecondary flow paths. Thus, the quantity of condenser tubing requiredfor an apparatus for practicing the present invention, as compared toapparatus presently well known in the art, is substantially reduced. Itis estimated that a reduction of approximately fifty percent in thequantity of condensing tubing required may be realized in makingapparatus to practice the present invention. Since the cost of condensertubing constitutes about one-third of total plant cost, the reduction ofcapital expenditure is appreciable.

I claim:

ll. A process for the distillation of a feed liquid con taining salt ina multi-stage distillation apparatus including a plurality ofsuccessively staged flash evaporation chambers each having a flashliquid zone and a vapor zone, each liquid zone except the last being influid communication with the next downstream liquid zone to provide aprogressive liquid flow path in one direction through the chambers, saidprocess comprising the steps of maintaining the liquid zones attemperatures progressively decreasing in said one direction to flash theliquid in each of the liquid zones whereby to produce vapor in each ofthe vapor zones, dividing the liquid to be distilled comprising bothfeed liquid and recycle liquid into a plurality of parts, treating atlest one of said parts with a scale inhibitor, tapping liquid from saidparts to provide a plurality of streams of liquid to be distilled, themajority of said streams of liquid to be distilled comprising a selectedblend of feed liquid and recycle liquid and a minority comprising feedliquid with scale inhibitor tapped from said parts, conveying eachstream of feed liquid along a primary flow path passing progressivelythrough a plurality of said vapor zones in heat exchange relationtherewith and in a direction opposite said one direction tosimultaneously cool the vapor in said vapor zones and preheat the feedliquid in each of said streams, diverting each stream from said primaryflow path in the vapor zone of the associated one of said chambers toand along a secondary flow path and in said one direction to anassociated flash liquid zone in another of said downstream chamberswherein the salt concentration of the liquid entering said other chamberliquid zone from the preceding chamber liquid zone is substantiallyequal to the salt concentration of the diverted stream, said step ofdiverting to be performed when the temperature of the stream to bediverted is substantially equal to the temperature of the liquidentering said other chamber liquid zone from said preceding chamberliquid zone, and collecting distillate obtained on condensation of vaporformed in said vapor zones.

2. A process as set forth in claim 1 wherein said liquid to be distilledincludes distillate from said process, said distillate comprising one ofsaid parts.

3. A process as set forth in claim 1 wherein the step of maintaining theliquid zones is further characterized as maintaining the liquid in eachliquid zone at a temperature below the temperature at which scaleforming materials therein tend to precipitate.

4. A process as set forth in claim 1 wherein the step of treating atleast one of said parts with scale inhibitor is further characterized astreating at least one of said parts with acid.

5. A process as set forth in claim 1 further characterized by said stepof diverting being performed when the temperature of the stream to bediverted is below the temperature at which scale forming materialstherein tend to precipitate.

6. A process as set forth in claim 5 including the additional step ofregulating flow of liquid from each said stream to said associated flashliquid zone to continuously replenish flashed liquid partially convertedto vapor in said associated flash liquid zone to maintain asubstantially constant quantity of flash liquid in said associated flashliquid zone.

7. A process as set forth in claim 5 including the additional step ofregulating flow of feed liquid from each said stream to its associatedflash liquid zone to permit feed liquid to flow from said stream intosaid associated flash liquid zone without substantially altering thepressure in said other chamber.

8. A process as set forth in claim 5 including the additional step offurther heating said feed liquid containing scale inhibitor after it hasbeen preheated by passing progressively through the vapor zones andbefore it is conveyed to said flash liquid zones.

9. A process as set forth in claim 5 including the additional step offurther heating at least some of said streams comprising said primaryflow path by passing the latter streams through an external heat sourceafter said latter streams have passed progressively through some of saidvapor zones and before passing said latter streams through the remainingvapor zones.

10. A process as set forth in claim 5 including the additional step ofpreheating the feed liquid before passing it progressively through saidvapor zones.

11. A process as set forth in claim 10 wherein the step of preheatingsaid feed liquid is further characterized as preheating said feed liquidbefore passing it progressively through the remainder of said vaporzones to increase the temperature of the lowest temperature streamsubsequent to said preheating to be diverted to a temperaturesubstantially equal to the temperature of the liquid entering the liquidzone of the last of said successively staged chambers from the liquidzone of the preceding chamber.

P0405) v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTEQN ,wBatentN ou 3 ,734,8351@ Y Dated May 22, 1973 Inventor) M Attilio Spicacci Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

C01. 4, line 24, "4th" should be 46th Col 4, line 32, "toe" should be-to--.

Signed and sealed this 20th day of November 1973.

v (SEAL) Attest:

EDWARD M.FLE'ICHER,JR. RENE D. TEGTMEYER Attestinq Officer ActingCommissioner of Patents

2. A process as set forth in claim 1 wherein said liquid to be distilledincludes distillate from said process, said distillate comprising one ofsaid parts.
 3. A process as set forth in claim 1 wherein the step ofmaintaining the liquid zones is further characterized as maintaining theliquid in each liquid zone at a temperature below the temperature atwhich scale forming materials therein tend to precipitate.
 4. A processas set forth in claim 1 wherein the step of treating at least one ofsaid parts with scale inhibitor is further characterized as treating atleast one of said parts with acid.
 5. A process as set forth in claim 1further characterized by said step of diverting being performed when thetemperature of the stream to be diverted is below the temperature atwhich scale forming materials therein tend to precipitate.
 6. A processas set forth in claim 5 including the additional step of regulating flowof liquid from each said stream to said associated flash liquid zone tocontinuously replenish flashed liquid partially converted to vapor insaid associated flash liquid zone to maintain a substantially constantquantity of flash liquid in said associated flash liquid zone.
 7. Aprocess as set forth in claim 5 including the additional step ofregulating flow of feed liquid from each said stream to its associatedflash liquid zone to permit feed liquid to flow from said stream intosaid associated flash liquid zone without substantially altering thepressure in said other chamber.
 8. A process as set forth in claim 5including the additional step of further heating said feed liquidcontaining scale inhibitor after it has been preheated by passingprogressively through the vapor zones and before it is conveyed to saidflash liquid zones.
 9. A process as set forth in claim 5 including theadditional step of further heating at least some of said streamscomprising said primary flow path by passing the latter streams throughan external heat source after said latter streams have passedprogressively through some of said vapor zones and before passing saidlatter streams through the remaining vapor zones.
 10. A process as setforth in claim 5 including the additional step of preheating the feedliquid before passing it progressively through said vapor zones.
 11. Aprocess as set forth in claim 10 wherein the step of preheating saidfeed liquid is further characterized as preheating said feed liquidbefore passing it progressively through the remainder of said vaporzones to increase the temperature of the lowest temperature streamsubsequent to said preheating to be diverted to a temperaturesubstantially equal to the temperature of the liquid entering the liquidzone of the last of said successively staged chambers from the liquidzone of the preceding chamber.